Method for determining signal quality in optical transmission systems
View Patent ↗A method for determining signal quality in optical transmission systems, wherein the effective signal-to-noise ratio is determined by measuring amplitude histograms of a signal and by calculating characteristic histogram moments and additional interference is ascertained by comparing the characteristic histogram moments with the optical signal-to-noise ratio.
1. A method for determining signal quality in optical transmission systems by measuring an amplitude histogram of a signal, the method comprising the steps of:
calculating characteristic histogram moments from the measured amplitude histogram;
measuring directly an optical signal-to noise ratio from the signal;
comparing the characteristic histogram moments with the measured optical signal-to-noise ratio; and
determining, a proportion of non-linear noise if the comparison yields non-correspondence, wherein a relationship between the characteristic histogram moments and signal-to-noise ratio is determined using the following:
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μ
1
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μ
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2
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=
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(
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-
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where μ 0 and μ 1 are average values of the amplitude distribution of the logic “1's” and “0's”, σ 0 and σ 1 are standard deviations of the amplitude distribution of the logic “1's” and “0's”, OSNR is signal-to-noise ratio, <P> av is an average signal power,
B
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is an optical bandwidth, B el is an electrical bandwidth of a photodiode or an opto-electrical transducer, and =ηq/hv is detector sensitivity (η=quantum efficiency, q=elementary charge, h=quantum of action, v=frequency of the signal).
2. A method for determining signal quality in optical transmission systems by measuring an amplitude histogram of a signal as claimed in claim 1 , the method further comprising the steps of:
determining a difference between the average values of the amplitude distributions regarded as Gaussian distribution for logic “1's” and logic “0's”;
determining a difference between variances of the amplitude distributions for logic “1's” and logic “0's”; and
determining a histogram moments term by forming a quotient from the two differences.
3. A method for determining signal quality in optical transmission systems by measuring an amplitude histogram of a signal as claimed in claim 1 , wherein, as the amplitude histogram, measurement is made of one of an error rate distribution in dependence on a variable sampling threshold, or a distribution density of logic “0's” or logic “1's” in dependence on the variable sampling threshold, or a probability density distribution of sampling amplitudes of logic “0's and logic “1's,” and wherein the characteristic histogram values are respectively determined in each case.
4. A method for determining signal quality in optical transmission systems by measuring an amplitude histogram of a signal as claimed in claim 1 , wherein the corresponding histogram moments are calculated in dependence on a signal-to-noise ratio of a transmission system having no link interference influences.
5. A method for determining signal quality in optical transmission systems by measuring an amplitude histogram of a signal as claimed in claim 1 , wherein the corresponding histogram moments are calculated in dependence on a signal-to-noise ratio without link interference influences for an optimum system.
6. A method for determining signal quality in optical transmission systems by measuring an amplitude histogram of a signal as claimed in claim 3 , wherein the corresponding histogram moments and associated signal-to-noise ratios are stored.
7. A method for determining signal quality in optical transmission systems by measuring an amplitude histogram of a signal as claimed in claim 4 , wherein the corresponding histogram moments and associated signal-to-noise ratios are stored.
8. A method for determining signal quality in optical transmission systems by measuring an amplitude histogram of a signal as claimed in claim 2 , wherein a function of the corresponding histogram moments is stored in dependence on the signal-to-noise ratio.
9. A method for determining signal quality in optical transmission systems by measuring an amplitude histogram of a signal as claimed in claim 3 , wherein a function of the corresponding histogram moments is stored in dependence on the signal-to-noise ratio.
10. A method for determining signal quality in optical transmission systems by measuring an amplitude histogram of a signal as claimed in claim 1 , wherein the term
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is determined by measurement.